Sum of squares
- Analysis of variance
- Basel problem
- Brahmagupta–Fibonacci identity
- British flag theorem
- Descartes' theorem
- Explained sum of squares
- Fermat's theorem on sums of two squares
- Heron's formula
- Hilbert's seventeenth problem
- Integer triangle
- Jacobi's four-square theorem
- Lack-of-fit sum of squares
- Lagrange's four-square theorem
- Least squares
- Legendre's three-square theorem
- Mean squared error
- Multivariate analysis of variance
- Partition of sums of squares
- Polynomial SOS
- Pythagorean prime
- Pythagorean quadruple
- Pythagorean theorem
- Pythagorean triple
- Rational trigonometry
- Reduced chi-squared statistic
- Residual sum of squares
- Square pyramidal number
- Squared deviations from the mean
- Squaring the square
- Sum of reciprocals
- Sum-of-squares optimization
- Sums of powers
- Total sum of squares